Where a number of radio systems are used in close proximity to one another, a relatively high power signal transmitted from one of the systems can swamp the signals received by other systems, even where the systems are operating at different transmission frequencies. The resulting desensitisation of a receiver impairs the ability of the receiver to receive and demodulate the incoming signal. Clearly, therefore, in these circumstances, communications difficulties can be faced, for example disrupting the reception of voice communications which may hamper organisation of personnel, or disrupting the reception of transmitted data signals. Depending upon the nature of the signals, the reception of which is disrupted, personnel may be put at unnecessary or avoidable risk.